Surface coatings containing effect pigments, such as light absorbing pigment, light scattering pigments, light interference pigments, and light reflecting pigments are well known. Metallic flake pigments, for example aluminum flakes, are examples of such effect pigments and are especially favored for the protection and decoration of automobile bodies, such as for example by reason of their imparting a differential light reflection effect, usually referred, to as “flop”, as well as flake appearance effects, which include flake size distribution and the sparkle imparted by the flake as well as the enhancement of depth perception in the coating. The flop effect is dependent upon the angle from which the car body is viewed. The degree of the flop effect achieved, is a function of the orientation of the metallic flakes with respect to the outer surface of the coating. The degree of sparkle is a function of the flake size, surface smoothness, orientation, and uniformity of the edges. Metallic coatings usually also contain pigments, generally of a light absorbing rather than a light scattering type. Any light scatter from the pigments or the flakes themselves, e.g., from the flake edges, diminishes both the flop and the sparkle of the coating.
For repairing a previously coated substrate, for example, of an automotive body, it is necessary to choose the correct pigments to match the color of that substrate as well as the correct effect pigments such as flakes to match the color and appearance of that substrate. Many coating formulas are made available by paint suppliers to match various vehicles and objects to be coated. Often there are multiple coating formulas available for the same vehicle make and model because of vehicle coating color and appearance variability due to slight variations in formulations, ingredients used, coating application conditions such as coating application techniques or locations used by vehicle original equipment manufacturers. These color and appearance variations make it difficult to identify the best formula to attain excellent matches in autobody shops. A number of methods have been developed to identify formulas of correct pigments to achieve color match. For example, U.S. Pat. No. 5,668,633 disclosed a computer implemented method for identifying one or more color formulas matching the color of a standard by using color spectrum readings. European patent application EP 1139234, filed on Feb. 12, 2001, disclosed a method to identify one or more color matching formulas to match color of a vehicle using a vehicle identification number (VIN) and a color code of that vehicle.
Some attempts were made to match both color and appearance of a target coating. U.S. Pat. No. 6,952,265, disclosed a method to obtain appearance data of a target coating in digital images and to compare the appearance data to appearance characteristics stored in a coating database. However, it lacks the ability to correlate color data and cannot identify formula for matching both color and appearance. WO 2006/030028, filed on Sep. 16, 2005 with an international application No. PCT/EP2005/054627, disclosed a method using color and texture properties of paint modules to formulate a coating for matching both color and appearance. However, it considers each of the properties individually and lacks capability to consider complex relations among each of the properties when mixed in a coating. A U.S. Pat. No. 6,959,111, disclosed a method for matching color of a target coating by obtaining color data in L*,a*,b* values by using a calorimeter, and quantitative particle feeling data by using a CCD camera. However, it requires the production of multiple test panels coated with a plurality of candidate coatings and repeated measurements of color and particle feeling data of the test panels to select best match on color and appearance.
It is therefore still in need for a method and a system for automatic measurement of appearance of a target coating and for the selection, from multiple existing coating formulas, of one or more matching formulas that closely match both the color and appearance of the target coating.